Synucleinopathies are a diverse group of neurodegenerative disorders that share a common pathologic characteristic: in neuropathologic examinations characteristic lesions can be detected containing abnormal aggregates of alpha-synuclein (alpha-syn) protein in selected populations of neurons and glia cells. Alpha-syn (initially identified as PARK1 and PARK4) is a 140 amino acid protein widely expressed in the neocortex, hippocampus, dentate gyrus, olfactory bulb, striatum, thalamus and cerebellum. Alpha-Syn is also highly expressed in hematopoietic cells including B-, T-, and NK cells as well as monocytes and platelets. The exact role in these cells is not known but it has been implicated in the differentiation of megakaryocytes (platelet precursors).
The most common synucleinopathies include but are not limited to Lewy body disorders (LBDs) like Parkinson's disease (PD), Parkinson's disease with dementia (PDD) and dementia with Lewy bodies (DLB), as well as Multiple System Atrophy (MSA) or Neurodegeneration with Brain Iron Accumulation type I (NBIA Type I). The current treatment options for these diseases include symptomatic medications such as L-dopa, anticholinergic drugs as well as inhibitors of monoamine oxidase. However, all treatment opportunities currently present only lead to symptomatic alleviation but do not induce a long lasting, disease modifying effect in patients.
Lewy body disorders (LBD) are progressive neurodegenerative disorders characterized by tremor, rigidity, bradykinesia and by loss of dopaminergic neurons in the brain. In the case of DLB and PDD signs also include cognitive impairment. Up to 2% of the population above 60 years of age in western countries develop the typical signs of PD/LBD. Currently only symptomatic treatment is available. Unfortunately, these therapies only provide temporary relief from early symptoms and do not halt disease progression.
The pathogenesis of PD/LBD is still incompletely understood, but it appears that genetic susceptibility and environmental factors are involved in the development of the disease. Despite all genetic advances, PD/LBD is primarily a sporadic disorder with no known cause (also called idiopathic PD/LBD). Patients suffering from this disease develop characteristic ubiquitinated intracellular inclusions called Lewy bodies (LBs) in the cortical and subcortical areas of the brain. Especially regions with high content of dopaminergic neurons or neuronal projections show this typical pathologic feature.
Recently, several studies could show that the synaptic protein alpha-syn plays a central role in LBD pathogenesis. In LBD, alpha-syn accumulates in LBs throughout affected brain areas. Additionally, it could be demonstrated that single point mutations as well as duplications or multiplications in the alpha-syn gene are associated with rare familial forms of parkinsonism. Importantly, based on results from overexpression studies in transgenic (tg) mice as well as in Drosophila melanogaster its key role in the pathogenesis of PD/LBD is underscored as these animal models mimic several characteristics of PD.
Another very important synucleinopathy is Multiple System Atrophy (MSA). MSA is a sporadic neurodegenerative disorder that is characterised by symptoms of L-DOPA-resistant parkinsonism, cerebellar ataxia, and dysautonomia. Patients suffer from multisystem neuronal loss affecting various brain areas including striatum, substantia nigra, cerebellum, pons, as well as the inferior olives and the spinal cord. MSA is characterized by alpha-syn-positive glial cytoplasmic (GCI) and rare neuronal inclusions throughout the central nervous system. These inclusions are associated with striatonigral degeneration, olivopontocerebellar atrophy, and involvement of autonomic nuclei in medulla and spinal cord. The importance of GCIs for the pathogenesis of MSA is generally acknowledged and underscored by recent analysis of transgenic mouse models analysing the effect of alpha-syn overexpression in oligodendroglia. In tg mice overexpressing human alpha-syn both GCI-like aggregates and biochemical markers of MSA were observed.
Although the exact mechanisms by which accumulation of alpha-syn leads to the typical features of neurodegeneration in synucleopathies and the characteristic symptoms of synucleopathies are not fully understood, recent studies imply that abnormal formation and accumulation of oligomers of alpha-syn are involved in the degenerative processes underlying synucleinopathy. It is currently believed that such oligomer-formation for example in the synaptic terminals and axons plays an important role for PD/LBD development. Hence reduction of alpha-syn deposition and oligomerisation should be beneficial in the treatment of synucleopathies, especially of idiopathic LBD/PD and MSA and could present the first strategy for treatment of these neurodegenerative diseases in addition to the mere alleviation of symptoms resulting from current treatment strategies like L-DOPA application.
In Iwatsubo T. (Neuropathology 27 (5)(2007): 474-478) the correlation of alpha-synuclein depositions as well as its phosphorylation with a pathogenesis of alpha-synucleopathies is examined. The author of this publication found that serine 129 of alpha-synuclein deposited in synucleopathy lesions is extensively phosphorylated.
US 2007/213253 relates to mutant human alpha-synuclein as well as peptides derived therefrom which may be used for inhibiting the aggregation of the wild-type human alpha-synuclein.
In the WO 2004/041067 means and methods for preventing or treating diseases associated with alpha-synuclein aggregation are disclosed which comprise the use of alpha-synuclein fragments.
In the US 2003/166558 peptides are described which can be used to induce immune response to protein deposits.
US 2005/198694 relates to alpha-synuclein fragments comprising at least 100 amino acids and having a C-terminal deletion of 1 to 23 amino acids.
Although experimental therapies utilizing neurotrophic factors and grafting of dopaminergic cells have yielded promising results, alternative approaches designed to reduce the neuronal accumulation of alpha-syn are required.
Recently, active and passive immunotherapy has become of increasing interest as a potential new treatment strategy for neurodegenerative diseases like Alzheimer's disease (AD), Prion Disease, as well as Chorea Huntington and Amyloid Lateral Sclerosis (ALS). For example, recent studies in tg mouse models of AD have shown that antibodies against beta-amyloid 1-42 (Aβ) promote the removal of amyloid from the brain, resulting in improved cognitive performance. Importantly, Aβ molecules are mainly located extracellularly and thus are constituting epitopes accessible to the immune system. In contrast to such ‘classical’ targets for immunotherapy, experiments have been performed to evaluate the potential of immunotherapy in reducing accumulation of intracellular pathogenic molecules. Vaccination approaches targeting prion protein and huntingtin have been shown to be effective in neurons of tg mice at reducing the accumulation of both molecules that, like alpha-syn, accumulate intracellularly. In addition recent experiments also describe anti-Tau and anti-SOD1 therapies as novel treatment strategies against intracellular pathogenic protein aggregates in AD and ALS respectively. Thus, there is compelling evidence accumulating that intracellular aggregates in brain cells might be targeted by immunotherapy. Indeed, recently a similar potential for the treatment of synucleopathies has been shown. Tg mice overexpressing human alpha-syn were vaccinated with human alpha-syn protein. In mice that produced high relative affinity antibodies upon vaccination, there was decreased accumulation of aggregated alpha-syn in neuronal cell bodies and synapses which was associated with reduced neurodegeneration. Furthermore, antibodies produced by immunized animals also detected abnormal aggregated forms of alpha-syn associated with the neuronal membrane and promoted the degradation of these aggregates, probably via lysosomal pathways. Similar effects were observed using passive immunotherapy with an exogenously applied alpha-syn-specific antibody. These results suggest that vaccination is effective in reducing neuronal accumulation of alpha-syn aggregates and that further development of this approach might elicit beneficial effects in the treatment of LBD and synucleinopathies.